1. Field of the Invention
The present invention generally relates to a substrate processing apparatus for improving a surface roughness on a resist film on a substrate, such as a semiconductor wafer.
2. Description of the Related Art
Generally, the photolithography step in a semiconductor device manufacturing process includes a resist application process, an exposure process, a developing process, and an etching process. In the resist application process, a resist solution is applied to an underlayer film on a semiconductor wafer, thereby forming a resist film. In the exposure process, the wafer surface is exposed to light to form a predetermined circuit pattern thereon. In the developing process, the exposed wafer is developed using a developing solution. In the etching process, the underlayer film or the like on the wafer is etched.
On the surface of the resist pattern after the aforementioned developing process, multiple lines appear in the horizontal and vertical directions on the side wall surfaces of the resist pattern due to the wave property of light (with the wavelength of 248 nm in the case of KrF and 193 nm in the case of ArF), with which the wafer surface is irradiated during the exposure process. These lines produce surface roughness called line width roughness (LWR) and line edge roughness (LER) on the resist pattern. When there is such roughness on the resist pattern surface, etching the underlayer film using the resist pattern as a mask causes the appearance of lines or other roughness on the underlayer film corresponding to the lines on the resist pattern. Thus, the lines or other roughness on the resist pattern prevent the formation of a precise circuit pattern and the manufacture of semiconductor devices with required quality.
The applicants have proposed a technology to overcome the aforementioned problems of LWR and LER. The technology, which is a smoothing process, employs a resist solvent vapor to dissolve and smooth the upper-most surface of the resist pattern (Japanese Laid-Open Patent Application No. 2005-19969; see the claims and FIGS. 4 and 5 in particular).
In accordance with this smoothing process, the solvent vapor is discharged via a nozzle onto the surface of a substrate having a resist pattern that has been exposed and developed. The solvent vapor swells the resist pattern and flattens the surface roughness.
In this smoothing process, in order to prevent the diffusion of the solvent vapor atmosphere within equipment, considerations must be given to the air-tight sealing and evacuation of the smoothing processing apparatus (module), and other safety precautions such as explosion proofing. An exhaust cup is typically provided within the apparatus so as to prevent the diffusion of the solvent vapor atmosphere within the apparatus.
However, it is difficult with the exhaust cup alone to reliably collect the solvent vapor discharged out of the nozzle, and the solvent vapor may still leak within the apparatus. Furthermore, prevention of diffusion of the solvent vapor from within the apparatus to the outside requires a sufficient air-tight sealing of the module.
When the solvent vapor remains in the nozzle, this may interfere with the subsequent processes. Thus, the solvent vapor used in a process needs to be collected without delay.